Solar cooling apparatus

ABSTRACT

A solar powered cooling apparatus utilizes a solar collector to convert radiant energy into heat stored in water. An evacuated chamber houses a dessicant bed and a sprayer which introduces an adsorbate into contact with a heat exchanger conduit extending within the chamber. Evaporation of the adsorbate in contact with the conduit cools a medium circulated within the conduit between the chamber and a chilled water reservoir. The evaporated adsorbate is adsorbed by the dessicant bed until a predetermined temperature or saturation level is reached, at which point, heated water from the solar collector is passed through heat exchanger conduits in the dessicant bed to regenerate the dessicant bed. Iterative adsorption and regeneration cycles maintain the chilled water in a desired temperature range.

FIELD OF THE INVENTION

The present invention relates to the use of solar energy as a source ofpower for cooling or refrigeration. More particularly the presentinvention relates to the use of solar energy as a means for regeneratingan adsorption cooling unit. In even greater particularity the presentinvention may be described as an adsorption cooling apparatus which usessolar heated water to regenerate a dessicant cooling bed.

BACKGROUND OF THE INVENTION

The phenomenon of adsorption cooling is well documented. Such coolingwas the basis of the so-called gas refrigerators which used a flammablegas to evaporate a liquid refrigerant such as ammonia from a solution sothat the ammonia could be condensed in purer form to serve as anevaporative heat sink. Many other variations have doubtlessly beenattempted. Due to the toxic nature of ammonia, many other refrigerantshave been substituted and due to the difficulty in locating flammablegases at remote areas, most cooling and refrigeration in the U.S. todayis done by electrically powered compression refrigeration. This isparticularly true with respect to home air-conditioning units for whichmy invention is particularly well suited.

SUMMARY OF THE INVENTION

It is the object of my invention to provide efficient economical coolingof a defined volume such as a home.

Another object of my invention is to provide a cooling system whichderives its primary energy requirements from solar energy.

Yet another object of my invention is to eliminate the need for toxicrefrigerants in a home cooling system.

Still another object of my invention is to provide a system which may beadapted to provide solar powered refrigeration.

These and other objects and advantages of my invention are accomplishedthrough the use of an efficient solar collector, preferably a collectorwhich tracks the movement of the sun such as is disclosed in myco-pending application Ser. No. 758,422. The solar collector convertsradiant solar energy into heat contained within a volume of water whichis stored in the system. The heated water is used as needed to"regenerate" a dessicant bed as hereinafter described.

The dessicant bed is contained within a low pressure chamber wherein thepartial pressure of water is maintained in a desired range whichfacilitates the boiling of water at a low temperature, for example 59°at a partial pressure of 0.50 inches of mercury. The dessicant bed isinterlaced with a heat exchanger conduit network which supplies water asa heat exchanger medium from either the solar collector in aregeneration mode or an ambient temperature heat source such as acooling tower in a cooling mode. Also contained within the chamber is asprayer for injecting water into the chamber and a second heat exchangerconduit network which utilizes water as a heat exchange medium from achilled water reservoir. Water from the sprayer is directed onto thesecond heat exchanger network and extracts sufficient heat therefrom toboil the water, thereby cooling the medium. The resultant water vaporsare adsorbed by the dessicant, retrieving heat from the first heatexchanger network. When the dessicant becomes saturated, hot water fromthe solar collector is forced through the first heat exchanger network,thereby giving up heat to the dessicant bed and driving the adsorbedwater back into vapor. Meanwhile, cooler water from the ambienttemperature heat source is circulated through the second heat exchangernetwork resulting in condensation of the water vapor which is collectedin an adsorbate collection chamber for recirculation through thesprayer. Through the use of multiple stages and the introduction ofsimple antifreeze solution to the heat transfer medium the endtemperature can be reduced below 32° F. The only energy input to thesystem other than solar energy is used to drive pumps in the heatexchanger networks and sprayer assembly, which represents a considerablereduction in the energy required to cool a home or freeze water.

BRIEF DESCRIPTION OF THE DRAWINGS

Apparatus embodying features of my invention are depicted in theappended figures which form a portion of this application and wherein:

FIG. 1 is a schematic representation of a solar cooling apparatus whichcan be used for home cooling;

FIG. 2 is a schematic representation of the electrical circuit of theapparatus;

FIG. 3 is a schematic representation of a multi-stage solar cooling unitwhich can be used for refrigeration-type cooling.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to FIG. 1, a solar air-conditioning unit 10 would include asolar collector and storage system 11, which is the primary source ofenergy input to the unit 10 and is hereinafter referred to as inputsystem 11. Input system 11 may be any solar powered system which canheat water and maintain it at above 140° F. Such results are readilyachieved with my solar tracker as disclosed in my co-pending applicationSer. No. 758,422 filed July 24, 1985 and which is incorporated herein byreference.

A conduit type input heat exchanger network 12, containing water as aheat exchanger medium, extends from the input system 11 into a housing13 which defines a low pressure chamber within which a dessicant bed 14is confined. The heat exchanger network 12 extends within the dessicantbed 14 to the extent necessary for efficient heat exchange given thegenerally low thermal transfer characteristics of dessicants. Thepreferred adsorbent for use in the dessicant bed 14 is a silica gelwhich offers excellent adsorption characteristics for this application.The heat exchanger network 12 includes an input pump 16 which isoperated to circulate hot water through the input system 11 to thedessicant bed 14.

An ambient temperature heat exchanger unit 18, which may be a trulyambient heat exchanger or a common variant such as an evaporativecooling tower having a fan 19 and sump 21, is connected to the inputheat exchanger network 12 by conduits 22. A cooling pump 23 is used tocirculate water from the ambient temperature heat exchanger unit 18through the dessicant bed 14. Check valve 17 prevents circulation fromthe ambient temperature heat exchanger unit 18 to the input system andcheck valve 24 prevents flow from the input system 11 to the ambienttemperature heat exchanger unit 18.

An adsorbate pumping unit 25 introduces and removes the adsorbate fromthe chamber. Located within the lower portion of the housing 13 is asprayer 26 which receives and disperses water from an adsorbatecollection tank 27 via an adsorbate pump 28. The collection tank 27communicates with the bottom of housing 13 through a conduit 29 suchthat any water accumulated therein is drained by gravity into thecollection tank 27. Obviously, the bottom of the housing 13 ispreferentially inclined toward conduit 29. The housing 13 is maintainedat a sub-atmospheric pressure, therefore adsorbate pump 28 ispreferentially a magnetically driven pump capable of providingsufficient flow to the sprayer 26 without compromising the low pressurewithin the housing.

Also extending into the housing 13 is a conduit type chilled water heatexchanger network 31 which also uses water as the heat exchange medium.This network 31 circulates water through a chilled water reservoir 32into the housing 13 proximal the sprayer 26 such that water sprayedthereby comes into contact with the network 31. A chilled water pump 35is operated to provide the flow through the heat exchanger network 31and reservoir 32.

A second set of conduits 33 connects the ambient temperature heatexchange unit 18 with the chilled water heat exchange network 31 and asecond cooling pump 34 circulates water between the housing 13 and theambient temperature heat exchange unit 18. Check valve 37 preventscirculation of water from the heat exchange unit 18 by the chilled waterpump 35 and a check valve 38 prevents circulation of water throughchilled water reservoir 32 by the second cooling pump 34. The reservoir12 has an outlet 39 and a return 41 through which chilled water issupplied to a house in conventional manner to cool the air therein.

Referring to FIGS. 1 and 2, it will be seen that a first thermostat 46is located in the housing 13 to sense the temperature of the dessicantbed 14. This thermostat 46 has an input terminal 47 connected to anelectrical power source and two output terminals 48 and 49. Outputterminal 48 is electrically connected to input pump 16 and secondcooling pump 34. Output terminal 49 is electrically connected to asecond thermostat 51 which is located in reservoir 32 and senses thetemperature of the chilled water. The thermostat 51 has a single outputterminal 52 which is normally open and which is electrically connectedto first cooling pump 23, adsorbate pump 28 and chilled water pump 35.

In operation, with silica gel used as the dessicant, and distilled waterused as the adsorbate, the housing 13 is maintained under asub-atmospheric pressure such that the water partial pressure has valueof about 0.40 to about 0.50 inches of mercury. In this range of partialpressures, water boils at from about 53° F. to about 59° F. At themidpoint of the range or about 0.45 inches of mercury, the boiling pointof water is 56° F. Silica gel is a poor thermal conductor however itscapacity to hold adsorbed water is proportional to the temperature ofthe silica gel. Thus a dessicant bed in an atmosphere where the waterpartial pressure is 0.40 inches of mercury at 140° F. has the capacityto hold a water content at about 4% of the weight of the bed and at 95°F. has the capacity to hold a water content at about 14% of the weightof the bed. In as much as the cooling capability of the system isdependent on the amount of water vaporized in the housing, it is clearthat the size of the housing and the weight of the dessicant bed 14 willbe proportional to the amount of cooling required.

A description of one cycle of operation of the system illustrates theabove correlations. As a starting point, assume that the temperature ofthe dessicant bed 14 has just reached 140° F. At that point, thethermostat 46 connects the electrical power source to thermostat 51 viaoutput terminal 49. When the temperature of the chilled water inreservoir 32 reaches 63° F., the thermostat 51 closes and suppliescurrent to pumps 23, 28 and 35. The chilled water pump 35 circulateswater within heat exchanger network 31 into housing 13 wherein adsorbatepump 28 delivers distilled water to the sprayer 26 such that the watercan be sprayed onto the heat exchanger network 31. The water sprayedthereon is boiled off at 56° F. in the low pressure chamber, therebyextracting heat from the circulating water in the heat exchanger network31 which in turn extracts heat from the chilled water in reservoir 32.The water vapor created by this boiling passes into the porous dessicantbed 14 and is adsorbed releasing heat to the dessicant bed 14, howevercooling pump 23 circulates water from the ambient temperature heatexchanger unit 18 through the dessicant bed to remove the heat ofadsorption and to cool the dessicant bed 14. The input temperature ofthe water from unit 18 to the dessicant bed is approximately 85° F.which is readily maintained by most conventional cooling towers in mostlocales. When the temperature of the chilled water in reservoir 32reaches 60° F., the thermostat 51 opens and the pumps 23, 28 and 35stop. This sequence is repeated until the temperature of the dessicantbed 14 is lowered to about 95° F., at which point the thermostat 46opens output terminal 49 and closes output terminal 48 thereby supplyingelectrical current to pumps 16 and 34. Input pump 16 circulates water atabove 140° F. through the input heat transfer network 12 which heats thedessicant bed 14 thereby reducing the bed's capacity to hold water andforcing the water back into vapor. Meanwhile cooling pump 34 iscirculating water at 85° F. through the portion of the chilled waterheat exchanger network 31 within the housing 13, thereby causing thewater driven from the dessicant bed 14 to condense, giving up heat to bedispersed by the cooling tower. The water accumulates in the bottom ofthe housing 13 from which it drains into accumulation tank 27. When thetemperature of the dessicant bed reaches 140° F., the bed is deemed tohave been purged of moisture and is thus regenerated and ready to begina new cooling cycle, thus the thermostat 46 opens to output terminal 49and closes to output terminal 48. The cycle is repeated for as long asnecessary. Of course, sufficient hot water for regeneration must bestored in the input system 11 to permit regeneration during the night.The rate at which the apparatus cycles depends on the rate of flow ofthe adsorbate pump 28 and the capacity of the dessicant bed 14 as wellas the efficiency of the input heat exchanger network 11 in regeneratingthe dessicant bed, thus the cycle time depends on the physicalparameters of the unit which is in turn dependent upon the utilizationof the unit. A prototype used for cooling purposes has been found tooperate satisfactorily with a cycle time of about one hour equallydivided between regeneration time and cooling time. The energyrequirement to drive the pumps is less than is necessary to burn five100 watt light bulbs.

FIG. 3 illustrates a multi-stage unit which can be used to furtherreduce the output temperature. In this embodiment, a second dessicantchamber 61 maintains a second dessicant bed 62 at a lower water partialpressure such that water introduced by a second adsorbate pumping unit63 boils at a lower temperature. For example, in a system with a waterpartial pressure of 0.20 inches of mercury, water boils at 35° F. and ina system with a water partial pressure of 0.10 inches of mercury, waterboils at 20° F. A regeneration heat exchanger network 64 extends throughthe second dessicant bed 62 and circulates water from either the ambienttemperature heat exchanger unit 18 or input system 11. A secondreservoir 66 for a refrigerant is provided and a tertiary heat exchangernetwork 67 is provided between the second chamber 61 and secondreservoir 66 in the same manner as chilled water heat exchanger network31 is provided between housing 13 and reservoir 32. Inasmuch as lowertemperatures are being used, it may be necessary to use a mixture ofwater and antifreeze (alcohol) as the refrigerant or medium in the heatexchanger conduits of this stage. The extraction of heat from the seconddessicant bed 62 during the cooling phase and the condensation of theadsorbate during the regeneration phase of the cycle utilizes anauxiliary heat exchanger conduit 68 system connected to circulaterefrigerant cooled within reservoir 32 through the regeneration conduitnetwork 64 and the tertiary conduit network 67 in the same manner asdescribed with respect to conduits 22 and 33 above. Appropriate pumps69, 71, 72 and 73 are used to circulate the refrigerant and check valves(not shown) are used to insure proper flow. Thermostats 74 and 76control the operation of these pumps and second adsorbate pump 77.

While I have shown my invention in various forms, it will be obvious tothose skilled in the art that it is not so limited but is susceptible ofvarious changes and modifications without departing from the spiritthereof.

What I claim is:
 1. Apparatus for cooling a desired volume of spacecomprising:(a) input means for heating water to a predeterminedtemperature by solar energy and storing said water at or above saidtemperature; (b) chamber means for housing a quantity of dessicant at asub-atmospheric pressure; (c) reservoir means for holding chilled water;(d) adsorbate means for introducing and removing water from said chambermeans; (e) first heat exchanger means for circulating water through saidinput means and through said dessicant in said chamber means; (f) secondheat exchanger means for circulating water through said reservoir meansand a portion of said chamber means proximal said adsorbate means; (g)ambient temperature heat exchanger means for cooling the water in saidfirst or second heat exchanger means operably connected to divert waterselectively from said first or second heat exchanger means; (h) circuitmeans for controlling water flow through said first and second heatexchanger means and said adsorbate means responsive to the temperaturein said chamber means and said reservoir means; and (i) output meansconnected to said reservoir means for circulating chilled water thereinto cool said volume.
 2. Apparatus as defined in claim 1 wherein saidcircuit means comprises:(a) a first thermostat connected to said chambermeans for sensing the temperature therein and having an input terminalconnected to a source of electrical current and a first and secondoutput terminal selectively connected to said input terminal inaccordance with the temperature sensed; (b) an input pump connected tosaid first output terminal for circulating water in said first heatexchanger means between said input means and said chamber means; (c)first cooling pump electrically connected to said first output terminalfor circulating water in said second heat exchanger means between saidchamber means and said ambient temperature heat exchanger means; (d)second thermostat connected to said reservoir means for sensing thetemperature of the chilled water therein and having an input terminalelectrically connected to the second output terminal of said firstthermostat and a normally open output terminal; (e) adsorbate pumpelectrically connected to said normally open output terminal forintroducing water into said chamber via said adsorbate means; (f)chilled water pump electrically connected to said normally open outputterminal for circulating water within said second heat exchanger meansbetween said chamber means and said reservoir means; and (g) secondcooling pump electrically connected to said normally open outputterminal for circulating water in said first heat exchanger meansbetween said chamber means and said ambient temperature heat exchangermeans.
 3. Apparatus as defined in claim 2 wherein said ambienttemperature heat exchanger is a cooling tower.
 4. Apparatus as definedin claim 2 wherein said dessicant is silica gel and said sub-atmosphericpressure is maintained in a range from about 0.40 atmospheres to 0.50atmospheres.
 5. Apparatus as defined in claim 4 wherein said firstthermostat connects said source of electric current to said first outputterminal when the temperature in said chamber means reachesapproximately 95° F. and connects said source of electrical current tosaid second output terminal when the temperature of said chamber meansreaches approximately 140° F.
 6. Apparatus as defined in claim 1 whereinsaid dessicant is silica gel and said sub-atmospheric pressure ismaintained in a range from about 0.40 atmospheres to 0.50 atmospheres.7. Apparatus as defined in claim 6 wherein said first heat exchangermeans circulates water between said input means and said chamber meansto raise the temperature of said dessicant bed from about 95° F. toabout 140° F.
 8. Apparatus as defined in claim 1 wherein said first heatexchanger means comprises a water filled primary conduit extendingwithin said dessicant and with said input means, an input pump connectedto said primary conduit for circulating water therein, a water filledsecondary conduit connected between said primary conduit and saidambient temperature heat exchanger means, a first cooling pump connectedto said secondary conduit for circulating water between said chamber andsaid ambient temperature heat exchanger means; and said second heatexchanger means comprises a water filled main conduit extending withinsaid reservoir means and said chamber means, a chilled water pumpconnected to said main conduit for circulating water therein, a waterfilled auxiliary conduit connected between said main conduit and saidambient temperature heat exchanger means, and a second cooling pumpconnected to said auxiliary conduit for circulating water between saidchamber and said ambient temperature heat exchanger.
 9. Apparatus asdefined in claim 8 wherein said adsorbate means comprises a gravitycollector cooperatively positioned beneath said chamber means forcollecting water condensed therein, sprayer means connected to saidgravity collector for dispersing water therefrom proximal said mainconduit with said chamber means, and an adsorbate pump connected to urgewater from said gravity collector to said sprayer means.
 10. Apparatusas defined in claim 1 wherein said circuit means comprises:(a) firstthermostat positioned to sense the temperature of said dessicant withsaid chamber means having an electrical input terminal connected to asource of electrical power and first and second output terminalsselectively connected to said input terminal in accordance with thetemperature of said dessicant, with said first output terminalelectrically connected to said input pump and said first cooling pump;and (b) a second thermostat positioned to sense the temperature of saidchilled water in said reservoir means and having an input terminalelectrically connected to said second output terminal and having anormally open output terminal connected to said chilled water pump, tosaid second cooling pump, and to said adsorbate pump.
 11. Apparatus asdefined in claim 10 wherein said dessicant is silica gel and saidsub-atmospheric pressure is maintained in a range from about 0.40atmospheres to 0.50 atmospheres.
 12. Apparatus as defined in claim 11wherein said first thermostat connects said source of electric currentto said first output terminal when the temperature in said chamber meansreaches approximately 95° F. and connects said source of electricalcurrent to said second output terminal when the temperature of saidchamber means reaches approximately 140° F.
 13. Apparatus as defined inclaim 1 wherein said chamber means comprises a housing for containingsaid dessicant at sub-atmospheric pressure having a dessicant bedlocated in the upper portion of said housing in thermal communicationwith said first heat exchanger means and an evaporator region located inthe lower portion thereof wherein said adsorbate means and said secondheat exchanger means are positioned proximal each other.
 14. Apparatusas defined in claim 1 wherein said output means comprises:(a) secondchamber means for housing a quantity of dessicant at a lowersub-atmospheric pressure; (b) second reservoir means for holding arefrigerant; (c) second adsorbate means for introducing and removingrefrigerant into said second chamber; (d) secondary heat exchanger meansfor circulating water through said ambient temperature heat exchangermeans and said dessicant in said second chamber means; (e) tertiary heatexchanger means for circulating refrigerant through said secondreservoir means and said second chamber means wherein said refrigerantis a mixture of water and alcohol; and (f) auxiliary cooling means forselectively extracting heat from said dessicant in said second chamberor for extracting heat from said refrigerant in said tertiary heatexchanger means by circulation thereof through said reservoir means. 15.Apparatus as defined in claim 14 wherein said circuit meanscomprises:(a) first thermostat positioned to sense the temperature ofsaid dessicant with said chamber means having an electrical inputterminal connected to a source of electrical power and first and secondoutput terminals selectively connected to said input terminal inaccordance with the temperature of said dessicant, with said firstoutput terminal electrically connected to said input pump and said firstcooling pump; and (b) a second thermostat positioned to sense thetemperature of said chilled water in said reservoir means and having aninput terminal electrically connected to said second output terminal andhaving a normally open output terminal connected to said chilled waterpump, to said second cooling pump, and to said adsorbate pump. 16.Apparatus as defined in claim 15 wherein said dessicant is silica geland said sub-atmospheric pressure is maintained in a range from about0.40 atmospheres to 0.50 atmospheres.
 17. Apparatus as defined in claim16 wherein said first thermostat connects said source of electriccurrent to said first output terminal when the temperature in saidchamber means reaches approximately 95° F. and connects said source ofelectrical current to said second output terminal when the temperatureof said chamber means reaches approximately 140° F.